Buggy code:
public class CustomizableTraceInterceptor extends AbstractTraceInterceptor { public static final String PLACEHOLDER_METHOD_NAME = "$[methodName]" ; public static final String PLACEHOLDER_TARGET_CLASS_NAME = "$[targetClassName]" ; public static final String PLACEHOLDER_TARGET_CLASS_SHORT_NAME = "$[targetClassShortName]" ; public static final String PLACEHOLDER_RETURN_VALUE = "$[returnValue]" ; public static final String PLACEHOLDER_ARGUMENT_TYPES = "$[argumentTypes]" ; public static final String PLACEHOLDER_ARGUMENTS = "$[arguments]" ; public static final String PLACEHOLDER_EXCEPTION = "$[exception]" ; public static final String PLACEHOLDER_INVOCATION_TIME = "$[invocationTime]" ; private static final String DEFAULT_ENTER_MESSAGE = ( ( ( "Entering<seq2seq4repair_space>method<seq2seq4repair_space>'" + ( CustomizableTraceInterceptor . PLACEHOLDER_METHOD_NAME ) ) + "'<seq2seq4repair_space>of<seq2seq4repair_space>class<seq2seq4repair_space>[" ) + ( CustomizableTraceInterceptor . PLACEHOLDER_TARGET_CLASS_NAME ) ) + "]" ; private static final String DEFAULT_EXIT_MESSAGE = ( ( ( "Exiting<seq2seq4repair_space>method<seq2seq4repair_space>'" + ( CustomizableTraceInterceptor . PLACEHOLDER_METHOD_NAME ) ) + "'<seq2seq4repair_space>of<seq2seq4repair_space>class<seq2seq4repair_space>[" ) + ( CustomizableTraceInterceptor . PLACEHOLDER_TARGET_CLASS_NAME ) ) + "]" ; private static final String DEFAULT_EXCEPTION_MESSAGE = ( ( ( "Exception<seq2seq4repair_space>thrown<seq2seq4repair_space>in<seq2seq4repair_space>method<seq2seq4repair_space>'" + ( CustomizableTraceInterceptor . PLACEHOLDER_METHOD_NAME ) ) + "'<seq2seq4repair_space>of<seq2seq4repair_space>class<seq2seq4repair_space>[" ) + ( CustomizableTraceInterceptor . PLACEHOLDER_TARGET_CLASS_NAME ) ) + "]" ; private static final Pattern PATTERN = Pattern . compile ( "\\$\\[\\p{Alpha}+\\]" ) ; private static final Set ALLOWED_PLACEHOLDERS = new Constants ( CustomizableTraceInterceptor . class ) . getValues ( "PLACEHOLDER_" ) ; private String enterMessage = CustomizableTraceInterceptor . DEFAULT_ENTER_MESSAGE ; private String exitMessage = CustomizableTraceInterceptor . DEFAULT_EXIT_MESSAGE ; private String exceptionMessage = CustomizableTraceInterceptor . DEFAULT_EXCEPTION_MESSAGE ; public void setEnterMessage ( String enterMessage ) throws IllegalArgumentException { } public void setExitMessage ( String exitMessage ) { } public void setExceptionMessage ( String exceptionMessage ) { } @ Override protected Object invokeUnderTrace ( MethodInvocation invocation , Log logger ) throws Throwable { } protected void writeToLog ( Log logger , String message ) { } protected void writeToLog ( Log logger , String message , Throwable ex ) { } protected String replacePlaceholders ( String message , MethodInvocation methodInvocation , Object returnValue , Throwable throwable , long invocationTime ) { } private void appendReturnValue ( MethodInvocation methodInvocation , Matcher matcher , StringBuffer output , Object returnValue ) { } private void appendArgumentTypes ( MethodInvocation methodInvocation , Matcher matcher , StringBuffer output ) { } private void checkForInvalidPlaceholders ( String message ) throws IllegalArgumentException { } private String escape ( String input ) { <START_BUG> StringBuffer sb = new StringBuffer ( ) ; <END_BUG> for ( int i = 0 ; i < ( input . length ( ) ) ; i ++ ) { char c = input . charAt ( i ) ; if ( c == '\\' ) { sb . append ( "\\\\" ) ; } else if ( c == '$' ) { sb . append ( "\\$" ) ; } else { sb . append ( c ) ; } } return sb . toString ( ) ; } }

Fix:
StringBuilder sb = new StringBuilder ( ) ;